1. Field of The Invention
This invention relates to novel compound semiconductors which are useful as light-emitting devices such as light-emitting diodes, semiconductor laser devices and the like. The invention also relates to light-emitting semiconductor devices using the novel compound semiconductors, which have emission wavelengths ranging from blue to ultraviolet regions of the spectrum.
2. Description of The Prior Art
Light-emitting diodes have been widely used as a display device, including red light-emitting devices using AlGaAs and green light-emitting devices using GaP. For the fabrication of multi-color display devices, there is a strong demand for blue light-emitting devices which can be used in practice. Such blue LEDs have not been in use yet. On the other hand, semiconductor lasers using AlGaAs/GaAs which are compound semiconductors of the groups III-V of the periodic table have been already utilized for pickup of signals from optical disks. If the emission wavelength of the pickup semiconductor laser is made small, the quantity of information memorizable in the disk can be increased, enabling the information processing capacity of the optical disk to be increased. In the fields of laser printers, if the lasing wavelength is made short, the sensitivity of sensitive materials can be improved with an attendant increase of the printing speed. Thus, the short emission wavelength of semiconductor lasers will lead to an improvement in performance of information processing devices and house-use devices. The shortest emission wavelength of hitherto known semiconductor lasers is in the range of 580 to 690 nm covering red to yellow light regions. For this purpose, AlGaInP compound semiconductors are used. In order to fabricate blue light-emitting semiconductor devices, studies have been made on Zn(SSe) materials which have a great forbidden band gap. However, the blue light-emitting device has not been fabricated successfully from the standpoint of practical applications because such materials involve a difficulty in control of the p-type conductivity.
In U.S. Pat. No. 5,008,891, there is proposed a semiconductor light-emitting device wherein an n-type II-VI compound semiconductor layer and a p-type chalcopyrite compound layer are formed on a compound semiconductor substrate.
At present, there is a demand for fabricating blue light-emitting devices with high brightness but such devices have not been realized yet. Where semiconductor lasers are utilized in information processing apparatus such as optical recording apparatus, laser printers and the like, the emission wavelength of the semiconductor laser should be as short as possible in order to increase the information processing capacity. However, with known semiconductor lasers using III-V compound semiconductors, it is not possible to obtain an emission wavelength ranging to the blue light region. When using II-VI compound semiconductors, blue to UV light emission which is continuous and stable has never been attained owing to the difficulty in control of the p-type conductivity. Therefore, there is a strong demand for semiconductor lasers which are suitable for practical applications and are able to emit wavelengths in the range of blue to ultraviolet regions.